1. Field of the Invention
This invention relates to a new process for the direct catalytic hydrogenation of glyceride oils using particulate and/or granulated catalysts containing copper chromite.
2. Statement of Related Art
The direct catalytic hydrogenation of glyceride oils has long been known from the literature. Processes such as these enable fatty alcohols--products of considerable commercial interest--to be directly obtained from fats and oils of natural origin. Hitherto, however, the process of direct hydrogenation has not been used to any significant extent in the commercial production of fatty alcohols. Instead, it has been preferred first to transesterify the glycerides of the native fats and oils with lower monoalcohols, preferably methanol, and then to subject the resulting fatty acid esters of lower alcohols to catalytic hydrogenation to form fatty alcohols. The valuable glycerol obtained in high yields and in high purity in this way ensures that the two-stage process is highly economical.
It is known from the prior art that water and propanol, rather than glycerol, are unexpectedly formed as secondary products in the one-stage process of direct hydrogenation of triglycerides (W. Nommann, Z. angewandte Chemie, 44(1931), 714-717). This is attributed to the fact that, under the prevailing reaction conditions, the glycerol initially formed enters into secondary reactions with elimination of water. The fact that it is not high-purity glycerol, but less valuable secondary products which are largely formed in the direct catalytic hydrogenation of glyceride oils by known processes means that this method of producing fatty alcohols cannot compete with the two-stage process in terms of economy. This is also the reason why the known processes for the direct hydrogenation of glyceride oils have not been adopted for working on an industrial scale.
Processes for the direct hydrogenation of triglycerides to higher aliphatic alcohols were also described in the patent literature, for example in U.S. Pat. Nos. 2,094,127; 2,109,844; and 2,241,417. In addition to the fatty alcohols corresponding in the length of the alkyl radicals to the C-chain length of the fatty acid residues, the processes disclosed in these U.S. patents, which are carried out at reaction temperatures of from 200.degree. to 400.degree. C. and under hydrogen pressures of from 100 to 300 bar, produce only small quantities of the desired reaction product glycerol and, instead, relatively large quantities of propane, propanol or propanediols.
German published application No. 16 68 219 describes a process for the hydrogenation of triglycerides from fats and oils, in which aluminum oxide and/or silicon dioxide catalysts promoted with iron, cobalt, molybdenum, chromium, tungsten or nickel are used for the hydrogenation at temperatures of from 300.degree. C. to 460.degree. C. and under pressures of up to 130 bar. This publication also mentions the danger of uncontrolled secondary reactions with formation of propylene glycol, propanol or propane instead of the valuable glycerol required. The controlled performance of the reaction at extremely high reaction temperatures and pressures is carried out to enable catalysts which, although comparatively inactive, are unaffected by catalyst poisons to be used for the hydrogenation and, in spite of this, to obtain glycerol as a secondary product. The use of copper chromite catalysts is specifically mentioned as unsuitable for the desired purposes. One disadvantage of this process is that selective product control to glycerol as a secondary product is only possible in a very narrow, but very high temperature and pressure range. Under the conditions mentioned, reduction of the fatty alcohols produced to the corresponding hydrocarbons is also observed in practice, jeopardizing the economy of the process through a reduction in yield. Another disadvantage lies in the fact that the catalysts used are not stable to traces of acid in the starting materials obtainable from native sources and, in addition, show inadequate mechanical strength, so that not only is separation of the solid catalyst from the reaction products extremely difficult, losses of active catalyst through erosion of catalyst material also have to be accepted. The need for continuous replenishment of active catalyst also jeopardizes the economy of the process.